Piezoelectric speaker

Abstract

A piezoelectric speaker improved in acoustic features by weight reduction of a diaphragm of the piezoelectric speaker without decreasing stiffness of the diaphragm or a coefficient of thermal expansion of surfaces of the piezoelectric speaker is provided. The diaphragm having placed thereon a piezoelectric element is made of a sandwich-laminate clad material using different materials. For example, surface materials made of 42 alloy each having a thickness of 10 μm and a core material made of aluminium having a thickness of 30 μm form a clad material having a thickness of 50 μm. The formed clad material is processed into an arbitrary shape to form the diaphragm of the piezoelectric speaker. With this diaphragm, it is possible to keep the stiffness and the coefficient of thermal expansion of the 42-alloy diaphragm having the thickness of 50 μm, and also achieve weight reduction by approximately 40%.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention relates to a piezoelectric speaker for acoustic equipment.[0003]2. Description of the Background Art[0004]Piezoelectric speakers are known as small-sized, low-current-driven acoustic components using a piezoelectric element as an electric acoustic conversion element, and are used as an acoustic output device for small-sized electric equipment. Generally speaking, the piezoelectric speaker has a structure such as that of a metal diaphragm pasted with a piezoelectric element having an electrode such as a silver film. An alternating voltage applied to both surfaces of the piezoelectric element deforms the piezoelectric element to vibrate the diaphragm, thereby producing sound.[0005]In conventional piezoelectric speakers, as disclosed in Japanese Patent Laid-Open Publication 2001-16692, for example, the diaphragm is supported so as to vibrate linearly, thereby flattening frequency characteristics. Ther...

AI Technical Summary

Benefits of technology

[0008]Therefore, an object of the present invention is to provide a piezoelectric speaker improved in acoustic features by weight reduction of a diaphragm of the piezoelectric speaker without decreasing stiffness of the diaphragm or a coefficient of thermal expansion of surfaces of the piezoelectric speaker.

[0011]According to the above structure, it is possible to achieve reduction in weight of the diaphragm by combining light-weight materials, compared with a diaphragm made of single material. Also, with the sandwich structure of different materials, the diaphragm having required stiffness can be easily designed. Therefore, the diaphragm can achieve required stiffness and light weight simultaneously. With such a light-weight diaphragm, the sound pressure level of the piezoelectric speaker can be improved.

[0012]The clad material may include two surface layers made of a first material to form both surfaces of the diaphragm; and a single core layer made of a second material that is different from the first material, and bonded between the two surface layers. With three-layer clad material made of two different materials, the diaphragm having the required stiffness can be easily designed and manufactured.

[0013]A coefficient of thermal expansion of the first material may be close to a coefficient of thermal expansion of the piezoelectric element. The density of the second material may be lower than a density of the first material. With this, it is possible to achieve a light-weight diaphragm having a coefficient of thermal expansion of the surface material of the diaphragm close to that of the piezoelectric element. Therefore, thermal exfoliation of the surface material from the piezoelectric element and thermal material destruction such as cracking can be avoided. That is, with the material having the core layer lighter in weight than that of the surface layers, it is possible to achieve a light-weight diaphragm having a coefficient of thermal expansion close to that of the piezoelectric element. Also, the surface layer may be thinner than the core layer. In this case, since the light-weight core layer forms a large proportion of the diaphragm, it is possible to achieve effects of further reducing the weight of the diaphragm.

[0014]The first and second materials may be ones selected out of a metal film and a film made of high polymer resin. This provides improved flexibility in selecting the materials for constructing the diaphragm. Furthermore, the first material may be the metal film made of 42 alloy stainless, and the second material may be one selected out of the metal film made of metal other than the 42 alloy stainless, and the film made of high polymer resin. Therefore, when the piezoelectric element is made of lead zirconate titanate (PZT) as generally used, the coefficient of thermal expansion of the surface layers becomes close to that of the piezoelectric element. With this construction, thermal exfoliation of the surface material from the piezoelectric element and thermal material destruction such as cracking can be avoided. Also, with the material of the core layer lighter in weight than 42 alloy stainless, it is possible to achieve a light-weight diaphragm having the coefficient of thermal expansion close to that of the PZT piezoelectric element. Still further, the second material may be a film made of aluminium. With the surface layers made of 42 alloy stainless and the core layer made of aluminium, it is possible to easily achieve the above-mentioned diaphragm.

[0015]Still further, the piezoelectric speaker may further include a frame portion surrounding the diaphragm; a damper portion connecting the frame portion and the diaphragm, and supporting the diaphragm so that the diaphragm can linearly vibrate; and an edge portion formed in an area delineated by the diaphragm, the damper portion, and the frame portion. The clad material having the layers made of the first and second materials laminated together may be subjected to a predetermined process to integrally form the diaphragm, the damper portion, and the frame portion. With the diaphragm, the damper portion, and frame portion integrally formed of the clad material, a speaker portion of the piezoelectric speaker can be easily formed. Still further, the edge portion may be formed by, for example, filling a material that is different from the first and second materials in a space formed among the diaphragm, the damper portion, and the frame portion. In this case, the edge portion for flattening frequency characteristics of the piezoelectric speaker can be appropriately formed. In another example, the edge portion may be formed by performing an etching process onto only the first material in the area delineated among the diaphragm, the damper portion, and the frame portion. In this case, the edge portion for flattening frequency characteristics of the piezoelectric speaker can be easily formed only by the etching process. Still further the frame portion may be provided with one electrode for applying a driving voltage to the piezoelectric element. In this case, when the frame portion is taken as one of electrodes, electricity is conducted to the diaphragm through the damper portion. Therefore, the piezoelectric element can be driven without taking the diaphragm as one of the electrodes. This can dispense with wiring directly to the diaphragm, thereby stabilizing vibration characteristics of the diaphragm.

Problems solved by technology

If the diaphragm is thinner than the above range, the stiffness of the diaphragm is decreased, causing difficulties in stably supporting the piezoelectric element and sufficiently converting shape distortion of the piezoelectric element into vibration.

Therefore, vibration of the diaphragm cannot be obtained, leading to a reduction in sound pressure level.

For this reason, the diaphragm of the conventional piezoelectric speaker cannot be made extremely thin for weight reduction because of the requirement of appropriate stiffness to maintain acoustic features.

Therefore, it has been difficult to achieve a reduction in weight of the diaphragm with different materials.

It has also been difficult to achieve an improvement in sound pressure level per unit energy that would have been brought by weight reduction.

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